What is a Photovoltaic system and How does it work ?

Photovoltaic system

             Solar photovoltaic system or solar power system is one of renewable energy systems.

 It uses PV modules to convert sunlight into electricity. The electricity generated can be either stored or used directly.

 It can be feedback into grid line or combined with one or more other electricity generators or more renewable energy sources.

 solar PV system is very reliable  and clean source of electricity.

It can be used a wide range of application such as residence, industry, agriculture, livestock.

Brief history of PV

             The photovoltaic effect was discovered in 1839 when 19 years old French physicist Edmond Becquerel. 

He discovered the photovoltaic effect with experimenting with an electrolytic cell made up of two metal electrodes.

In 1873 Willoughby smith discovered the photoconductivity of selenium and in 1876, Adams and Day observed the photovoltaic effect in solid selenium.

 Around 1870, a solar engine was developed by captain john Ericsson, which is used concave mirrors to gather enough solar radiation to drive a motor.

Albert Einstein published his paper on the photovoltaic effect. This paper described the phenomenon, for which he later received a Nobel prize.

Aside for Einstein Nobel winning documentation, the most critical technology developed came in 1941, when the first silicon mono crystallin solar cell was created.

The first silicon mono crystalline solar cell served as type of cell used most commonly found today.

In 11954, the PV effect is Cd was reported in as a commercial application; primary work was performed by Rappaport, jenny at RCA.

Bell labs researchers Pearson, Chapin and fuller reported their discovery of 4.5% efficient silicon solar cells.

 This was raised to 6% only a few months later by a work team including mort prince.

Chapin ,fuller, Pearson submitted their results to the journal of applied physics western electric began to sell commercial licenses for silicon PV technologies is 1955 Hoffman electronic semiconductor division announced a commercial PV product at 2% efficiency.

PV technology was initially used in satellites and some small devices, and only in the 1970 began  to be used in providing energy in commercial and private buildings. 

Since then the technology and availability. Since then the technology and availability have been improved and PV is now the fastest growing type of power generated technology in the world.

In 1972, solar power corporation was established. The company started commercial business in 1973. At Delaware university a photovoltaic - thermal hybrid system, solar one, one of the photo voltaic systems for domestic application was developed. 

In 1974 the Japanese sunshine project commenced. In 1975, Solar technology international were developed.

In 1976, under NASA protection, Lewis research center commenced photovoltaic systems systems installation for application on earth.

 The system were meant for refrigerators, Telecommunications Equipment, Lightening and water pumping power supply as well as for other applications. 

In 1977 , the world production of photovoltaics modules exceeded 500 kw. In 1979, ARCO solar of Camarillo, California, built the biggest solar cell.

In 1981 NASA  began to built system for vaccine refrigerator power supply at 30 locations around the globe. The world production of photovoltaic modules exceeded 9.3 MW in 1982.

In 1983, the world wide production of photovoltaic modules exceeded 21.3 Mw. In 1984 a 1mw photovoltaic power plant began to operate  in Sacramento, California. 

In 1989 BP solar received  a thin film technology patent solar cells. In 1990, energy conservation devices INC and canon INC,  established a joint company, united solar system corporation, for solar cell production.

Basic principle of PV

        Conversion of light energy into electrical energy is based on a phenomenon  called photovoltaic effect. Photovoltaic cell is the basic unit of the system where photovoltaic effect is utilized to produce electricity from light energy.

Silicon is the most widely used semiconductor material for constructing photovoltaic cell. 

When semiconductor materials are expected to light, the some of the photons of light ray are absorbed  by the semiconductors crystal which causes significant number of free electron in the crystal.

This is the basic reason of producing electricity due to photovoltaic effect. The solar cell consist of 1) P - type silicon material layer, 2) N- type silicon material layer, 3) Front metallic grid and 4) Opaque black metal contact.

When light falls on the active surface, photons with energy exceeding a certain  level known as band or energy gap interact with the valence electrons and elevate them to the conduction band. 

This activity also leaves holes so that the photons are said to generate " electron hole " pairs. These electron hole pairs are produced throughout the thickness of the silicon.

T he concentration depends on the intensity and spectral distribution of the light. The electrons move throughout the crystal.

 By the reverse field at a particular point the electrons are accelerated towards the negative contact and the holes towards the positive. A potential difference is established across the cell, and this will drive a current through an external load.

PV in Silicon

     Silicon has some special chemical properties, especially in its crystalline form. A silicon atom has 14 electrons, arranged in three different shells. 

The first two Shell which hold two and eight electrons respectively, both are completely full. The outer shell contains only 4 electrons.

A silicon atom will always try to fill up its last shell and for doing this, it will share electrons with four nearby atoms.

Each atom has four hands joined to four neighbors. That means, it is in the form of crystalline structure, and that structure, and that structure is important to constant PV cell.

The pure silicon is a poor conductor  of electricity  because none of its electrons are free to move. For making conductivity, proper impurities are added to it. 

The process of adding impurities is known as doping. The semiconductors doped by pentavalent impurity atoms is known as N type semiconductor.

Similarly the semi conductor doped by trivalent impurity atoms is known as P type semiconductor. The P type and N type semiconductor are combined together to form a PV cell. 

There is always a potential barrier between N type and P type materials. This potential barrier is essential for working of a photovoltaic or solar cell.